This invention relates to acoustic logging of boreholes and, more particularly, to a system for controlling an acoustic transducer to direct pulses of acoustic energy toward a borehole wall at a repetition rate synchronized with the rotational speed of the transducer within the borehole.
In U.S. Pat. Nos. 3,369,626 to Zemanek, Jr.; 3,718,204 to Groenendyke; and 3,728,672 to Dennis et al, there are disclosed methods of and apparatus for scanning the walls of a borehole with acoustic energy. In these patents a borehole televiewer logging tool employs a transmitter and a receiver of acoustic energy which are rotated within the borehole. The transmitter is cyclically energized to provide a beam of acoustic energy pulses for scanning the walls of the borehole. Reflected acoustic pulses are received by the receiver between transmitted acoustic pulses and are converted to reflection signals for recording on an electron beam display device. A sweep signal is generated each time the acoustic energy beam is rotated through a 360.degree. scanning pattern. Such sweep signal is applied to the horizontal deflection plates of the display device to sweep an electron beam horizontally across the face of the display device. The reflection signals are applied to the Z-axis of the display device to intensity modulate the electron beam as the beam is swept across the face of the display device to provide a picture which is a function of the time or distance from the transmitter and receiver to the wall of the borehole and of the density of the borehole wall.
In both the above-described patents the combination of transducer rotation along with vertical movement of the borehole televiewer logging tool along the length of the borehole results in a continuous spiral of the borehole wall being scanned. The resulting display is a picture of the density of the material forming the walls of the borehole at different depth points. This scanning of the borehole wall permits the determination of the actual configuration of the borehole. In addition, it permits the determination of anomalies which may exist at different depths in the borehole. For example, these anomalies may be a fault or a fracture in the formations traversed by the borehole.